Insights Into Interaction of Lutein with Pea Protein Isolate in Aqueous Nanometre-Scale Dispersion: Thermal Stability, Spectroscopic, and Morphological Properties

Attaining an appropriate color is a pivotal factor in achieving a desirable appearance for pea-based products. Although the color of lutein is vibrant, its stability during thermal processing remains a significant challenge that has yet to be overcome. A comprehensive understanding of the interactions between pea protein isolate (PPI) and lutein, as well as their influence on lutein retention and the solution behavior of PPI itself, is crucial for the development of pea protein-based products with optimized color. Currently, PPI provided a pronounced protective effect against the thermal degradation of lutein, primarily by influencing the retention rate, overall color variation, and total antioxidant capacity of lutein. Fluorescence spectroscopy revealed static quenching with strong affinity between PPI and lutein. The surface hydrophobicity of PPI after binding lutein decreased significantly (p < 0.05), while the secondary structure of PPI remained stable without notable relaxation or unfolding. Notably, lutein exists in both dispersed and aggregated forms, while the resulting lutein–PPI complex manifested as stable spherical nanoparticles. Polydispersity index and Z-average diameter measurements reveal that the lutein–PPI complex is more homogeneous and stable than PPI alone. In summary, compared to previous references, the present study fundamentally enhanced understanding of the underlying mechanisms involved in the interaction of PPI with lutein, thereby providing valuable insights for the development of novel plant-derived protein products with improved color stability.